It depends on how much time you have to give to it. If you don't have enough time to train in your other style at least three times a week, and enough of a commitment to keep it up for at least several years, I think it's a waste of time to get started. If you decide to attend a weekend seminar here and there where you get a little exposure to some other style, that's no doubt fine and will broaden your mind, but without a true commitment of time and effort, you can't be said to be "training" in another style.